In recent years, image forming apparatuses based on electrophotographic methods have been used as common copiers and printers in offices to print documents as well as for simple copying, and moreover have expanded their application to the area of preparing printed materials used outside offices, specifically to the print-on-demand (POD) market, which is included in the quick-printing market, since variable information from electronic data is readily printed. Accordingly, various copiers and printers have been installed in offices, resulting in increased power consumption as a whole.
In image forming apparatuses based on electrophotographic methods, since the most power is consumed during the fixing treatment, devices which require less energy in the fixing treatment have been in demand.
To realize energy conservation as described above, various proposals have been made so that enhanced low-temperature fixability can be realized via a toner composed of a binder resin exhibiting a low softening temperature. However, the toner composed of a binder resin exhibiting a low softening temperature has the problem of poor heat-resistant storage properties.
Further, in image forming based on electrophotographic methods, formation of color images, specifically formation of high quality color images exhibiting gloss to some extent or more has been in high demand.
There has been disclosed a binder resin composed of a crystalline polyester resin for use in a toner to form high quality color images (for example, refer to Patent Document 1). Further, there has been proposed a technique to realize enhanced low-temperature fixability via a urea-modified polyester resin as the polyester resin (refer, for example, to Patent Document 2).
However, in the POD market, high-speed printing is emphasized. Of course, a toner needs to be certainly fixed even in high-speed printing, but the following problems exist: high-speed fixability can not be achieved via the above toner employing a crystalline polyester resin, and further adequate high-speed fixability can not be achieved even via a toner featuring a structure wherein the core particle composed of the crystalline polyester resin is coated with a highly viscoelastic amorphous polyester resin.
Further, even though the toner employing a urea-modified polyester resin makes it possible to achieve low-temperature fixability, there is still the problem in that heat-resistant storage properties are degraded due to the decrease in crystallinity via urea modification.
(Patent Document 1) Japanese Patent Application Publication open to Public Inspection (hereinafter referred to as JP-A) No. 2006-91378
(Patent Document 2) JP-A No. 2005-250303